from previous posts and searching..
normal top bearings have a limit of 12,600rpm
the charger spins 1.6x crank speed on a 76mm normal pulley.
therefore at 6500rpm= charger spins at 10,400 rpm
76/65 = 17% smaller (ish)
therefore a 65mm pulley is 12,160rpm
a 60mm pulley is 13,173 rpm
a 58mm puley is 13,628 rpm
so the bartek ones be fine.
I've asked my supplier, who's gettin back to me with prices.
And yeah - viton seals i supply deal with heat better (and actually cost 10x price to have supplied rather than nitrile - black - ones)